Image Encoding Apparatus and Method, and Image Decoding Apparatus and Method

ABSTRACT

N (N≧2) time stretch units receive N channels of second image data which are obtained by dividing each line of first image data by N and are composed of a first number of bits. Each N time stretch unit arranges pixels of the N channels in the order of the pixels of the corresponding line of the first image data within a period which is obtained by stretching a one-line period of the second image data. The N time stretch units generate third image data including N lines of the first image data. N encoders encode each coding target pixel of the third image data outputted from the N time stretch units using a difference between the target pixel and a peripheral pixel to generate encoded data composed of a second number of bits which is smaller than the first number of bits.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority under35 U.S.C. §119 from Japanese Patent Application No. 2015-173545, filedon Sep. 3, 2015, the entire contents of which are incorporated herein byreference.

BACKGROUND

The present disclosure relates to image encoding apparatus and methodand image decoding apparatus and method using pixel-based predictioncoding.

The size of high-resolution digital image data is large. Processing suchdigital image data of large size requires large capacity memory andtransmission paths. Large capacity memory and transmission pathsincrease the cost. To reduce the capacities of memory and transmissionpaths, image encoding apparatuses are used to reduce the size of imagedata.

An image encoding apparatus described in Japanese Patent No. 5582019(Patent Document 1) converts a difference between a coding target pixeland a peripheral pixel into encoded data.

SUMMARY

Conventional digital image processing apparatuses such as liquid crystaldisplays typically handle full high-definition (Full HD) image data. Inrecent years, image data called 4K or 8K, including 4 or 16 times asmany pixels as that of Full HD data, has appeared and is becomingwidespread.

The size of 4K or 8K image data is larger than that of Full HD imagedata. It is therefore effective to convert image data to encoded datausing the image encoding apparatus to reduce the data size.

The dot clock frequency for 4K or 8K image data is much higher than thatfor Full HD image data. It is difficult for digital image processingapparatuses to operate with a high dot clock frequency. Each line of 4Kor 8K image data is therefore divided into plural channels. Each channelof data is processed with a comparatively low frequency dot clock.

An image encoding apparatus which calculates a difference between acoding target pixel and a peripheral pixel (a pixel adjacent to thetarget pixel, for example) like the image encoding apparatus describedin Patent Document 1, is configured to generate encoded data assumingprocessing of one channel of image data.

When image data is divided in plural channels, in some cases the codingtarget pixel is not correlated with the temporally adjacent pixel. Theimage encoding apparatus does not properly encode the image data andcannot encode plural channels of image data with high image quality.

A first aspect of the embodiments provides an image encoding apparatusto encode first image data in which each line includes a first number ofpixels, including: N time stretch units configured to arrange pixels ofN channels of second image data in the order of pixels in the respectivelines of the first image data, within a period obtained by stretching aone-line period of the second image data to generate third image dataincluding N lines of the first image data, the N channels of secondimage data being obtained by dividing the first image data by N andbeing composed of a first number of bits, the N being an integer equalto or greater than 2; and N encoders configured to encode each codingtarget pixel of the third image data outputted from the N time stretchunits, using a difference between the target pixel and a peripheralpixel to generate encoded data composed of a second number of bits,which is smaller than the first number of bits.

A second aspect of the embodiments provides an image encoding method toencode first image data in which each line includes a first number ofpixels, including: arranging pixels of N channels of second image datain the order of pixels in the respective lines of the first image data,within a period obtained by stretching a one-line period of the secondimage data to generate third image data including N lines of the firstimage data, the N channels of second image data being obtained bydividing the first image data by N and being composed of a first numberof bits, the N being an integer equal to or greater than 2; and encodingeach encoding target pixel of the third image data using a differencebetween the target pixel and a peripheral pixel to generate encoded datacomposed of a second number of bits, which is smaller than the firstnumber of bits.

A third aspect of the embodiments provides an image decoding apparatus,including: N decoders configured to decode each decoding target pixel ofN channels of encoded data, in which each line includes a first numberof pixels and that is composed of a first number of bits, using adifference between the target pixel and a peripheral pixel to generatefirst image data composed of a second number of bits which is largerthan the first number of bits, the N being an integer equal to orgreater than 2; N time compressors configured to distribute the pixelsincluded in each line of the first image data outputted from the Ndecoders, into parallel N channels within a period obtained bycompressing a one-line period of the first image data, to generate Nchannels of second image data; and N selectors configured to select therespective N channels of second image data outputted from the N timecompressors to generate N channels of third image data.

A fourth aspect of the embodiments provides an image decoding methodincluding: decoding each decoding target pixel of N channels of encodeddata, in which each line includes a first number of pixels, and that iscomposed of a first number of bits, using a difference between thetarget pixel and a peripheral pixel to generate first image datacomposed of a second number of bits, which is larger than the firstnumber of bits, the N being an integer equal to or greater than 2;distributing the pixels included in each line of the first image datainto parallel N channels within a period obtained by compressing aone-line period of the first image data, to generate N channels ofsecond image data; and generating N channels of third image data byselecting the respective N channels of second image data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an image encoding apparatusaccording to at least one embodiment.

FIG. 2 is a diagram illustrating a line of 4K image data.

FIG. 3 is a diagram illustrating a first example of image data in whicheach line of 4K image data is divided into four channels.

FIG. 4 is a diagram illustrating a second example of image data in whicheach line of 4K image data is divided into four channels.

FIG. 5 is a diagram for explaining the operation of time stretch units11 to 14 in FIG. 1 which receive the first example of image data.

FIG. 6 is a diagram for explaining the operation of time stretch units11 to 14 in FIG. 1 which receive the second example of image data.

FIG. 7 is a block diagram illustrating an image decoding apparatusaccording to at least one embodiment.

DETAILED DESCRIPTION

Hereinafter, a description is given of image encoding apparatus andmethod and image decoding apparatus and method according to theembodiment with reference to the accompanying drawings.

<Image Encoding Apparatus and Method>

The image encoding apparatus according to the embodiment is assumed toencode 4K image data in an example described herein. The image data tobe encoded has a resolution of 3840 pixels (horizontal) by 2160 pixels(vertical).

In FIG. 1, time stretch units 11 to 14 receive image data sets S0a, S0b,S0c, and S0d, which are obtained by dividing one channel of 4K imagedata into four channels.

As illustrated in FIG. 2, each line of the 4K image data includes 3840pixels, pixels d0 to d3839. 2160 lines in the image data aresequentially referred to as lines L1, L2, L3, and so on. Each line ofthe image data of one channel is divided into four channels toconstitute the image data sets S0a to S0d.

The image data sets S0a to S0d correspond to channels A to D,respectively.

FIG. 3 illustrates a first example of image data sets S0a to S0d of fourchannels. In the first example, the channels A to D are assignedcyclically to the pixels beginning with the pixel d0. The image data setS0a is composed of the pixels d0, d4, and so on to d3836. The image dataset S0b is composed of the pixels d1, d5, and so on to d3837. The imagedata set S0c is composed of the pixels d2, d6, and so on to d3838. Theimage data set S0d is composed of the pixels d3, d7, and so on to d3839.

Each of the image data sets S0a to S0d is composed of a line of 960pixels. All the image data sets S0a to S0d constitute the line L1, L2,L3, etc., which is composed of 3840 pixels.

FIG. 4 illustrates a second example of the image data sets S0a to S0d offour channels. In the second example, the pixels d0 to d959 are assignedto channel A. The pixels d960 to d1919 are assigned to channel B. Thepixels d1920 to d2879 are assigned to channel C. The pixels d2880 tod3839 are assigned to channel D.

The time stretch units 11 to 14 of FIG. 1 receive the image data setsS0a to S0d of the four channels illustrated in FIG. 3 or 4,respectively. Since the 4K image data is divided into four channels, theimage encoding apparatus only needs to operate at a dot clock for FullHD.

The time stretch units 11 to 14 temporally stretch the image data setsS0a to S0d in the following manner. FIG. 5 illustrates an operation whenthe time stretch units 11 to 14 temporally stretch the image data setsS0a to S0d of FIG. 3. FIG. 6 illustrates an operation when the timestretch units 11 to 14 temporally stretch the image data sets S0a to S0dof FIG. 4.

First, using FIG. 5, a description is given of an operation oftemporally stretching the image data sets S0a to S0d of FIG. 3.

As illustrated in FIG. 5, the time stretch unit 11 arranges the pixelsd0 to d3839 of the image data sets S0a to S0d, constituting the line L1in the order of pixels of the 4K image data, and outputs the image dataof the line L1 as an image data set S11.

The time stretch unit 12 arranges the pixels d0 to d3839 of the imagedata sets S0a to S0d, constituting the line L2 in the order of pixels ofthe 4K image data, and outputs the image data of the line L2 as an imagedata set S12.

The time stretch unit 13 arranges the pixels d0 to d3839 of the imagedata sets S0a to S0d, constituting the line L3 in the order of pixels ofthe 4K image data, and outputs the image data of the line L3 as an imagedata set S13.

The time stretch unit 14 arranges the pixels d0 to d3839 of the imagedata sets S0a to S0d, constituting the line L4 in the order of pixels ofthe 4K image data, and outputs the image data of the line L4 as an imagedata set S14. The time stretch units 11 to 14 then repeat the sameoperation.

The time stretch unit 11 outputs image data of the lines L1, L5, L9,etc., as the image data sets S11, and the time stretch unit 12 outputsimage data of the lines L2, L6, L10, etc., as the image data sets S12.

The time stretch unit 13 outputs image data of the lines L3, L7, L11,etc., as the image data sets S13, and the time stretch unit 14 outputsimage data of the lines L4, L8, L12, etc., as the image data sets S14.

In this process, the time stretch units 11 to 14 are configured tooutput the image data of each line L1, L2, L3, etc., within a periodwhich is longer than the one-line period of the image data sets S01 toS0d. For example, the time stretch units 11 to 14 temporally stretch theimage data to four times.

When the number of channels is N (N is an integer equal to or greaterthan 2), the time stretch units 11 to 14 temporally stretch image datato N times, but may stretch to less than N times.

Next, using FIG. 6, a description is given of an operation of temporallystretching the image data sets S0a to S0d of FIG. 4.

As illustrated in FIG. 6, the time stretch unit 11 arranges the pixelsd0 to d959 in the image data set S0a constituting the line L1, thepixels d960 to d1919 in the image data set S0b constituting the line L1,the pixels d1920 to d2879 in the image data set S0c constituting theline L1, and the pixels d2880 to d3839 in the image data sets S0dconstituting the line L1, in this order. The time stretch unit 11outputs the image data of the line L1 composed of the arranged pixels d0to d3839 as the image data S11.

Similarly, the time stretch unit 12 outputs the image data of the lineL2 composed of the arranged pixels d0 to d3839 as the image data S12.The time stretch unit 13 outputs the image data of the line L3 composedof the arranged pixels d0 to d3839 as the image data S13. The timestretch unit 14 outputs the image data of the line L4 composed of thearranged pixels d0 to d3839 as the image data S14. The time stretchunits 11 to 14 then repeat the same operation.

The time stretch unit 11 outputs image data of the lines L1, L5, L9,etc., as the image data sets S11, and the time stretch unit 12 outputsimage data of the lines L2, L6, L10, etc., as the image data sets S12.

The time stretch unit 13 outputs image data of the lines L3, L7, L11,etc., as the image data sets S13, and the time stretch unit 14 outputsimage data of the lines L4, L8, L12, etc., as the image data sets S14.

The time stretch units 11 to 14 similarly stretch the image data to Ntimes or less within a period longer than the one-line period of theimage data sets S0a to S0d.

The time stretch units 11 to 14 can be composed of a memory in which theimage data sets S0a to S0d are written and read out in the order ofarrangement of pixels as illustrated in FIG. 5 or 6.

Returning to FIG. 1, the image data sets S11 to S14 outputted from thetime stretch units 11 to 14 are inputted into encoders 21 to 24,respectively. The encoders 21 to 24 encode the image data sets S11 toS14 to generate encoded data sets S21 to S24, respectively. The encoders21 to 24 can employ the configuration described in Patent Document 1,for example.

The encoders 21 to 24 can be composed of a circuit composed of hardwarethat is configured to encode the image data sets S11 to S14 based on anencoding algorithm to generate the encoded data sets S21 to S24, orsoftware (a computer program).

The image data of the image data sets S11 to S14 of each line, which areinputted into the encoders 21 to 24, are the same as the correspondingline of the 4K image data set illustrated in FIG. 2. In the image datasets S11 to S14, the coding target pixel and the pixel temporallyadjacent to the target pixel are therefore correlated to each other. Theencoders 21 to 24 can therefore encode the image data sets S11 to S14appropriately with high image quality.

In the second example of the image data sets S0a to S0d illustrated inFIG. 4, the target pixel is correlated with the pixel temporallyadjacent thereto in most parts. Since one channel of image data isdivided into four channels, the image data cannot be properly encodedaround the separated pixels if the image data sets S0a to S0d aredirectly encoded by the encoders 21 to 24. This can result indegradation of the image quality.

The image encoding apparatus of the embodiment including the timestretch units 11 to 14 generates the encoded data sets S21 to S24 ofhigh image quality when receiving either the image data sets S0a to S0dof the first example, or the image data sets S0a to S0d of the secondexample.

Line memory 31 delays the encoded data S21 by a one-line period andsupplies the encoded data S21 delayed by a one-line period to theencoder 22. Line memory 32 delays the encoded data S22 by a one-lineperiod and supplies the encoded data S22 delayed by a one-line period tothe encoder 23.

Line memory 33 delays the encoded data S23 by a one-line period andsupplies the encoded data S23 delayed by a one-line period to theencoder 24. Line memory 34 delays the encoded data S24 by a one-lineperiod and supplies the encoded data S24 delayed by a one-line period tothe encoder 21.

The encoders 21 to 24 may be configured to select one of the pluralprediction modes. In this case, the line memories 31 to 34 also delayprediction mode indices by a one-line period and supply the predictionmode indices to the encoders 22 to 24 and 21, respectively. Theprediction mode indices indicate prediction modes selected by theencoders 21 to 24.

The line memories 31 to 34 are provided if the encoders 21 to 24respectively require the encoded data sets S24 and S21 to S23 delayed bya one-line period for encoding. The line memories 31 to 34 can beeliminated if the image encoding apparatus employs such an encodingmethod that the encoders 21 to 24 do not require the encoded data setsS24 and S21 to S23 delayed by a one-line period.

The encoded data sets S21 to S24 outputted from the encoders 21 to 24are arbitrarily processed, such as being stored in an unillustratedframe memory or are multiplexed for transmission. The encoded data setsS21 to S24 are of a smaller volume than the image data sets S0a to S0d.The memory and transmission paths can be therefore configured to have asmall capacity.

Herein, the time stretch units 11 to 14 are generalized as N timestretch units. The N time stretch units are configured to operate asfollows in the image encoding apparatus, according to the embodiment.

The N time stretch units receive N channels of second image data. The Nchannels of second image data are obtained by dividing each line offirst image data by N. Each line of the first image data includes afirst number of pixels. The second image data is composed of a firstnumber of bits.

Each N time stretch unit arranges pixels of the received N channels ofsecond image data in the order of the pixels of each line of the firstimage data, within a period which is obtained by stretching the one-lineperiod of the second image data. The N time stretch units therebygenerate third image data, including N lines of the first image data.The N lines are adjacent to each other.

Next, the encoders 21 to 24 are generalized as N encoders. The Nencoders are configured to operate as follows. The N encoders encodeeach coding target pixel of the third image data outputted from the Ntime stretch units using a difference between the target pixel and aperipheral pixel, to generate encoded data composed of a second numberof bits which is smaller than the first number of bits.

The line memories 31 to 34 are generalized as N line memories. The Nline memories are configured to operate as follows. Each of the N linememories delays the inputted encoded data by a one-line period, andsupplies the same to the encoder which generates encoded data of a linesubsequent to a line of the encoded data inputted to the line memory.

As described above, according to the image encoding method and apparatusaccording to the embodiment, it is possible to encode with high imagequality, plural channels of image data, obtained by dividing a channelof image data.

<Image Decoding Apparatus and Method>

In FIG. 7, decoders 41 to 44 receive the encoded data sets S21 to S24.The decoders 41 to 44 decode the encoded data sets S21 to S24 togenerate image data sets S41 to S44, respectively. The decoders 41 to 44can employ the configuration described in Patent Document 1.

The decoders 41 to 44 can be composed of a circuit composed of hardwarewhich is configured to decode the encoded data sets S21 to S24 based ona decoding algorithm to generate image data sets S41 to S44, or software(a computer program), respectively.

A line memory 51 delays the image data set S41 by a one-line period andsupplies the image data S41 delayed by a one-line period to the decoder42. A line memory 52 delays the image data S42 by a one-line period andsupplies the image data set S42 delayed by a one-line period to thedecoder 43.

A line memory 53 delays the image data set S43 by a one-line period andsupplies the image data set S43 delayed by a one-line period to thedecoder 44. A line memory 54 delays the image data set S44 by a one-lineperiod and supplies the image data set S44 delayed by a one-line periodto the decoder 41.

The decoders 41 to 44 may be each configured to select one of the pluralprediction modes. In this case, the line memories 51 to 54 also delaythe prediction mode indices selected by the decoders 41 to 44 by aone-line period, and supply the same to the encoders 42 to 44 and 41,respectively.

The line memories 51 to 54 are provided if the decoders 41 to 44 requirethe image data sets S44 and S41 to S43, delayed by a one-line period fordecoding, respectively. The line memories 51 to 54 can be eliminated ifthe image decoding apparatus employs such a decoding method that thedecoders 41 to 44 do not require the image data sets S44 and S41 to S43delayed by a one-line period.

Time compressors 61 to 64 perform a time compression operation for theinputted image data sets S41 to S44. The time compression operation isthe reverse of the time stretch operation described with FIG. 5 or 6.

To be specific, the time compressor 61 distributes the pixels d0 tod3839, constituting the line L1 to N parallel channels illustrated inFIG. 5 or 6, and outputs the same as image data sets S611 to S614corresponding to the image data sets S0a to S0d. The image data setsS611 to S614 are image data sets of the channels A to D, respectively.

The time compressor 62 distributes the pixels d0 to d3839 constitutingthe line L2 to the N parallel channels, and outputs the same as imagedata sets S621 to S624, corresponding to the image data sets S0a to S0d.The image data sets S621 to S624 are image data sets of the channels Ato D, respectively.

The time compressor 63 distributes the pixels d0 to d3839 constitutingthe line L3 to the N parallel channels, and outputs the same as imagedata sets S631 to S634 corresponding to the image data sets S0a to S0d.The image data sets S631 to S634 are image data sets of the channels Ato D, respectively.

The time compressor 64 distributes the pixels d0 to d3839 constitutingthe line L4 to N parallel channels, and outputs the same as image datasets S641 to S644, corresponding to the image data sets S0a to S0d. Theimage data sets S641 to S644 are image data sets of channels A to D,respectively. The time compressors 61 to 64 then repeat the sameoperation.

The time compressors 61 to 64 can be composed of a memory in which theimage data sets S41 to S44 are written and are divided into channels Ato D to be read.

The selectors 71 to 74 receive the image data sets S611 to S614, S621 toS624, S631 to S634, and S641 to S644.

The selector 71 selects the image data sets S611, S621, S631, and S641for channel A in the image data sets S611 to S614, S621 to S624, S631 toS634, and S641 to S644, and outputs the same as an image data set S7afor channel A.

The selector 72 selects the image data sets S612, S622, S632, and S642for channel B in the image data sets S611 to S614, S621 to S624, S631 toS634, and S641 to S644 and outputs the same as an image data set S7b forchannel B.

The selector 73 selects the image data sets S613, S623, S633, and S643for channel C in the image data sets S611 to S614, S621 to S624, S631 toS634, and S641 to S644 and outputs the same as an image data set S7c forchannel C.

The selector 74 selects the image data sets S614, S624, S634, and S644for channel D in the image data sets S611 to S614, S621 to S624, S631 toS634, and S641 to S644 and outputs the same as an image data set S7d forchannel D.

The selectors 71 to 74 can be composed of a circuit composed of hardwareor software (a computer program).

The image data sets S7a to S7d correspond to the image data sets S0a toS0a of FIG. 1 respectively, but are not completely the same as the imagedata sets S0a to S0d, due to errors generated in the coding and decodingprocesses.

Herein, the decoders 41 to 44 are generalized as N decoders. The Ndecoders are not configured to operate as follows.

The N decoders decode each decoding target pixel of N channels ofencoded data, which includes a first number of pixels in each line andis composed of a first number of bits, using a difference between thetarget pixel and a peripheral pixel. The N is an integer not less than2. The N decoders generate first image data composed of a second numberof bits which is larger than the first number of bits. The N channels ofencoded data include encoded data of adjacent N lines.

The time compressors 61 to 64 are generalized as N time compressors. TheN time compressors are configured to operate as follows. The N timecompressors distribute the pixels included in each line of first imagedata outputted from the N decoders, into parallel N channels within aperiod obtained by compressing a one-line period of the first image datato generate N channels of second image data.

The selectors 71 to 74 are generalized as N selectors. The N selectorsare configured to operate as follows. The N selectors select therespective N channels of the second image data outputted from the N timecompressors to generate N channels of third image data.

In some cases, a memory is provided before the image decoding apparatusillustrated in FIG. 7, to adjust the phase and data configuration ofencoded data to be supplied to the image decoding apparatus. In such acase, the configuration of the image decoding apparatus is properlychanged in accordance with the phase and data configuration of theencoded data.

According to the image decoding apparatus and method of the embodiment,plural channels of encoded data can be decoded into plural channels ofimage data that are obtained by dividing a channel of image data.

The present invention is not limited to the embodiment described above,and can be variously changed without departing from the scope of theinvention. In FIGS. 1 and 7, since N is set to 4, the image encoding anddecoding apparatuses include four each of the constituent components.The number of each constituent component may be set to a value inaccordance with N.

What is claimed is:
 1. An image encoding apparatus to encode first imagedata in which each line includes a first number of pixels, comprising: Ntime stretch units configured to arrange pixels of N channels of secondimage data in the order of pixels in the respective lines of the firstimage data, within a period obtained by stretching a one-line period ofthe second image data to generate third image data including N lines ofthe first image data, the N channels of second image data being obtainedby dividing the first image data by N and being composed of a firstnumber of bits, the N being an integer equal to or greater than 2; and Nencoders configured to encode each coding target pixel of the thirdimage data outputted from the N time stretch units, using a differencebetween the target pixel and a peripheral pixel to generate encoded datacomposed of a second number of bits, which is smaller than the firstnumber of bits.
 2. The image encoding apparatus according to claim 1,further comprising N line memories configured to delay the encoded dataoutputted from the respective N encoders by a one-line period, whereineach of the N line memories is configured to supply the encoded datadelayed by the one-line period to one of the N encoders which generateencoded data of a subsequent line to the encoded data inputted to theline memory.
 3. An image encoding method to encode first image data inwhich each line includes a first number of pixels, comprising: arrangingpixels of N channels of second image data in the order of pixels in therespective lines of the first image data, within a period obtained bystretching a one-line period of the second image data to generate thirdimage data including N lines of the first image data, the N channels ofsecond image data being obtained by dividing the first image data by Nand being composed of a first number of bits, the N being an integerequal to or greater than 2; and encoding each encoding target pixel ofthe third image data using a difference between the target pixel and aperipheral pixel to generate encoded data composed of a second number ofbits, which is smaller than the first number of bits.
 4. An imagedecoding apparatus, comprising: N decoders configured to decode eachdecoding target pixel of N channels of encoded data, in which each lineincludes a first number of pixels and that is composed of a first numberof bits, using a difference between the target pixel and a peripheralpixel to generate first image data composed of a second number of bitswhich is larger than the first number of bits, the N being an integerequal to or greater than 2; N time compressors configured to distributethe pixels included in each line of the first image data outputted fromthe N decoders, into parallel N channels within a period obtained bycompressing a one-line period of the first image data, to generate Nchannels of second image data; and N selectors configured to select therespective N channels of second image data outputted from the N timecompressors to generate N channels of third image data.
 5. The imagedecoding apparatus according to claim 4, further comprising N linememories configured to delay the first image data outputted from therespective N decoders by the one-line period, wherein the first imagedata delayed by the one-line period and outputted from the N linememories are supplied to the decoder generating a line of the firstimage data subsequent to the line of the first image data inputted tothe line memory.
 6. An image decoding method comprising: decoding eachdecoding target pixel of N channels of encoded data, in which each lineincludes a first number of pixels, and that is composed of a firstnumber of bits, using a difference between the target pixel and aperipheral pixel to generate first image data composed of a secondnumber of bits, which is larger than the first number of bits, the Nbeing an integer equal to or greater than 2; distributing the pixelsincluded in each line of the first image data into parallel N channelswithin a period obtained by compressing a one-line period of the firstimage data, to generate N channels of second image data; and generatingN channels of third image data by selecting the respective N channels ofsecond image data.